H. AVDU[INOVI] et al.: INFLUENCE OF INOCULATION METHODS AND THE AMOUNT OF AN ADDED INOCULANT ...833–836

INFLUENCE OF INOCULATION METHODS AND THE AMOUNTOF AN ADDED INOCULANT ON THE MECHANICAL

PROPERTIES OF DUCTILE IRON

VPLIV METOD MODIFIKACIJE IN KOLI^INE DODANEGAMODIFIKATORJA NA MEHANSKE LASTNOSTI DUKTILNEGA

@ELEZA

Hasan Avdu{inovi}1, Almaida Gigovi}-Geki}1, Diana ]ubela1,Raza Sunulahpa{i}1, Nermin Mujezinovi}2

1University of Zenica, Faculty of Metallurgy and Materials Science, Travni~ka cesta 1, 72000 Zenica, Bosnia and Herzegovina2CIMOS TMD CASTING, d. o. o., Zenica, Radna zona Zenica-1 bb, 72000 Zenica, Bosnia and Herzegovina

hasan.avdusinovic@famm.unze.ba

Prejem rokopisa – received: 2014-09-30; sprejem za objavo – accepted for publication: 2014-10-13

doi:10.17222/mit.2014.248

In most cases an addition of inoculants to molten cast iron is advisable and even necessary to produce good-quality castings.The mechanical properties and machinability of cast iron with nodular graphite greatly depend on the formation of graphite andthe matrix microstructure and both are significantly influenced by the inoculation treatment. The mechanism of inoculation, theinfluence of the inoculation method and the amount of added inoculants are presented.Keywords: ductile iron, inoculation, microstructure, graphite, metallic matrix

V ve~ini primerov je dodatek modifikatorjev staljenemu livnemu `elezu priporo~ljiv in celo potreben za izdelavo dobrih ulitkov.Mehanske lastnosti in obdelovalnost litega `eleza z nodularnim grafitom so mo~no odvisne od oblike grafita in odmikrostrukture osnove, na oboje pa mo~no vpliva obdelava z modifikatorji. Predstavljen je mehanizem modifikacije, vplivmetode modifikacije in vpliv koli~ine dodanega modifikatorja.Klju~ne besede: duktilno `elezo, inokulacija, mikrostruktura, grafit, kovinska osnova

1 INTRODUCTION

Inoculants are the materials added to molten castiron, modifying the microstructure and, thereby, chang-ing the physical and mechanical properties to a degreenot explained on the basis of the change in the compo-sition. Inoculation is a phase of the technological processof producing ductile iron that controls and improves themicrostructure and mechanical properties of castings.Through inoculation, graphite nucleation and eutecticundercooling of the melt can be controlled, which iscrucial for achieving the required service properties ofthe castings.1–3

The inoculant most commonly used in foundries is aferrosilicon alloy with precisely defined contents of Ca,Ba, Sr, Zr, Al and rare-earth elements. The benefits ofinoculations are: an improved machinability, increasedstrength and ductility, reduced hardness and fracture sen-sitivity, a more homogenous microstructure, a reducedtendency for solidification shrinkage, etc.

During modularizing, numerous inclusions with asulfide core and an outer shell containing complex mag-nesium silicates are formed. Such micro-inclusions donot provide an effective nucleation for graphite becausethe crystal lattice structure of magnesium silicates doesnot match sufficiently with the lattice structure of gra-

phite. After the inoculation with a ferrosilicon alloy con-taining Ca, Ba or Sr, the surfaces of the micro-inclusionsare modified and other complex Ca, Sr, or Ba silicatelayers are obtained. Such silicates have the same hexago-nal crystal lattice as graphite and act as effective nucle-ation sites for graphite nodules to grow during solidifica-tion.4

The required rate of adding inoculants to a liquid de-pends very much on the place and time of their inocula-tion.

2 EXPERIMENTAL PROCEDURE

In the investigations of the response of ductile-irontest melts to different amounts of added inoculants anddifferent inoculation methods, three types of the inocu-lation method were applied: the ladle inoculation, thein-stream inoculation and the in-mold inoculation. Thepartner foundry in this research project was "CimosTMD Casting" in Zenica.

In the first project step, 15 melts were prepared. Fulllists of the chemical compositions, the amounts of addedinoculants and the places of the inoculant introductionare included in Table 1. High-purity FeSi with additionsof Al, Ca, and Sr was used for the inoculation. The test

Materiali in tehnologije / Materials and technology 49 (2015) 5, 833–836 833

UDK 669.18:621.74 ISSN 1580-2949Professional article/Strokovni ~lanek MTAEC9, 49(5)833(2015)

iron melts were obtained using an induction furnace andcasting iron into a green-sand mold. After the casts werecooled down and cleaned, samples for the mechanical-property examination were prepared.1

The testing of the mechanical properties was per-formed according to BAS EN 100002:2002 relating totensile testing and BAS EN 6507-1/2007 relating tohardness testing of fractured tensile-test bars.

Based on the summary of the results of testing thecasting properties, conclusions about the optimumamounts of the added inoculants needed for obtaining therequired values of the mechanical properties, weredrawn.

Casting procedures involving the exact amounts ofthe added inoculants required for three different methods

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Table 1: Chemical compositions of the experimental melts, places of the inoculation and added amounts of the inoculants (first step of theproject)Tabela 1: Kemijska sestava eksperimentalnih talin, mesto dodajanja modifikatorja in koli~ina dodanega modifikatorja (prva stopnja projekta)

No. Chemical composition (%) Inoculant (%) Temp.°CC Si Mn P S Cr Cu Mg stream mold ladle

1 3.52 2.17 0.428 0.016 0.006 0.086 0.314 0.043 0 0 0 13882 3.51 2.20 0.433 0.016 0.006 0.090 0.314 0.040 0 0.05 0 13923 3.49 2.06 0.401 0.015 0.006 0.089 0.332 0.032 0 0.15 0 14024 3.58 2.15 0.403 0.014 0.005 0.076 0.346 0.043 0 0.20 0 14075 3.56 2.09 0.482 0.011 0.003 0.111 0.340 0.040 0.05 0.05 0 13956 3.44 2.11 0.485 0.012 0.003 0.095 0.356 0.047 0.05 0.10 0 14107 3.60 2.14 0.345 0.016 0.006 0.054 0.080 0.053 0.10 0 0 13808 3.54 2.10 0.337 0.017 0.009 0.071 0.090 0.055 0.05 0 0 13809 3.52 2.15 0.362 0.014 0.007 0.064 0.091 0.045 0.15 0 0 1390

10 3.56 2.11 0.398 0.017 0.008 0.068 0.316 0.047 0.10 0.05 0 140011 3.62 2.45 0.353 0.017 0.009 0.049 0.119 0.065 0.20 0 0 138712 3.65 2.11 0.392 0.019 0.012 0.054 0.149 0.079 0.15 0.05 0 140513 3.62 2.12 0.382 0.019 0.011 0.054 0.144 0.060 0 0.20 0 139014 3.61 2.11 0.357 0.018 0.009 0.037 0.187 0.048 0 0 0.05 139815 3.64 2.14 0.384 0.016 0.011 0.084 0.212 0.052 0 0 0.20 1402

Table 2: Range of the chemical compositions of the test melts (second step of the project)Tabela 2: Obseg kemijskih sestav preizkusnih talin (druga stopnja projekta)

Composition C Si Mn S P Mgw/% 3.4–3.6 2.1–2.3 0.2–0.4 0.003–0.012 0.01–0.02 0.003–0.055

Figure 3: In-mold inoculation, Nital etchedSlika 3: Modifikacija v kokili, jedkano v nitalu

Figure 2: In-stream inoculation, Nital etchedSlika 2: Modifikacija v curek, jedkano v nitalu

Figure 1: Ladle inoculation, Nital etchedSlika 1: Modifikacija v ponvi, jedkano v nitalu

of inoculation were conducted in the second step to findthe most suitable casting technology in the partnerfoundry. A total of 60 melts were prepared in the secondstep of the project and the average melt chemical com-position is presented in Table 2.

3 RESULTS AND DISCUSSION

Figures 1 to 3 show the microstructures of the sam-ples taken from the melts (castings) inoculated withdifferent methods; the tensile strengths and hardnessvalues are presented in Figures 4 and 5.

The required hardness was in the range of 180–220HB and the tensile strength was in the range of 500–550MPa. According to the results in Figures 1 and 2, thebest result was observed with the samples with 0.1 % ofthe inoculants. In the second project step we used 20

melts for each inoculation method, i.e., 60 melts weretreated with 0.1 % of the added inoculants. The mecha-nical properties are shown in Figures 6 and 7 and inTable 3.

4 CONCLUSIONS

Experimental materials with quite satisfactory cha-racteristics were prepared with vacuum induction melt-ing. The results obtained in the first project step showedthat with 0.1 % of the inoculant the targeted hardnessand tensile strength for the given ductile iron wereachieved.

In the second project step it was found that thein-stream inoculation ensured the best result as almost100 % of all the samples achieved the targeted values forthe hardness and tensile strength and the standard devi-ation was the smallest.

Acknowledgment

The authors would like to thank the Federal Ministryof Education and Science of the Federation of Bosnia

H. AVDU[INOVI] et al.: INFLUENCE OF INOCULATION METHODS AND THE AMOUNT OF AN ADDED INOCULANT ...

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Figure 7: Tensile-strength values of the tested samples (second step ofthe project); black horizontal bars – targeted valuesSlika 7: Natezna trdnost preizkusnih vzorcev (druga stopnja projekta);~rne vodoravne ~rte – ciljne vrednosti

Figure 5: Tensile-strength values of the tested samples (first step ofthe project)Slika 5: Natezna trdnost preizkusnih vzorcev (prva stopnja projekta)

Table 3: Average values and standard deviations of the hardness andtensile strength (second step of the project)Tabela 3: Povpre~ne vrednosti in standardna deviacija trdote innatezne trdnosti (druga stopnja projekta)

Hardness (HB) Tensile strength (MPa)Inoculation method In mold In

stream Ladle In mold Instream Ladle

Average 212.15 203.8 205.3 564.65 546.3 474.95St.

deviation 7.86 6.88 27.02 29.1 9.41 33.61

Figure 4: Hardness values of the tested samples (first step of theproject)Slika 4: Trdota preizkusnih vzorcev (prva stopnja projekta) Figure 6: Hardnes values of the tested samples (second step of the

project); black horizontal bars – targeted valuesSlika 6: Trdota preizkusnih vzorcev (druga stopnja projekta); ~rnevodoravne ~rte – ciljne vrednosti

and Herzegovina and Foundry "CIMOS TMD CAST-ING" in Zenica for their financial aid and cooperationduring the implementation of the research project.

5 REFERENCES1 H. Bornstein et al., Cast Metals Handbook, American Foundrymen’s

Society, Des Plaines, Illinois, USA 1957, 312 E. Fras, M. Gorny, Inoculation Effects of Cast Iron, Archives of

Foundry Engineering, 12 (2012) 4, 39–463 J. N. Harvey, G. A. Noble, Inoculation of Cast Irons – An Overview,

55th Indian Foundry Congress, India, 2007, 343–3604 T. Skaland, A New Approach to Ductile Iron Inoculation, American

Foundry Society, Schaumburg, Illinois, USA 2001

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